WHITEPAPER
3D Printing
Techniques and Rapid Prototyping
B.Diallo
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INTRODUCTION
The primary driving factor for the adoption of 3D printing techniques in the development of products is that 3D printing is an additive manufacturing process.
Traditionally, products are constructed using a subtractive process that involves removing material from an object until it creates the desired part. Products that are manufactured with this method are most mass produced items.
Although accurate to the needed requirements, these methods produce waste and many components require multiple machining runs to reach the desired specifications. Additionally, for producing prototypes and proof of concepts, the costs associated can be high due to the nature of reiterations during the design process and expensive tooling machines used.
3D printing instead works through building millimetre thick layers using a variety of different materials such as carbon, nylon, metal and different plastics. Many more materials are continuing to be developed to meet manufacturing needs.
The promise of producing full products at home is not yet realized, nevertheless, rapid developments are happening in other areas, namely all the major engineering fields such as the automotive field, aerospace, mechanical engineering and civil engineering.
The aim of this white-paper is to highlight the most utilised 3D printing techniques and explore the qualities that each technique has. This paper will highlight material choices and both the strength and weakness of each printing technique in the context of rapid prototyping within an organisation.
3D PRINTING PROCESS
The 3D printing process involves steps that need to be taken before the creation of a prototype or end-use product.
CAD software has been one of the biggest contributors to the advancement of 3D printing technologies. It is used in nearly all product development processes in some form or another. It is a crucial tool that creates 3D objects that can help product development teams test and adjust key elements in a product before shipping.
The 3D printing process has become easier due to the advancement of software that can make use of the technology.
STEP 1
CAD
Computer Aided Design (CAD) is software that allows for the construction of objects in a virtual environment. Examples include Auto desk, Solidworks and many others.
STEP 2
STL
The STL file format is the most widely used file format for 3D printers. It converts 3D models into a readable format for the printer. If your STL model is rough, so will be your printed object.
STEP 3
3D Printer Type
Setup depends on the printer type, where FDM is a plastic filament that is melted, SLA is resin based and SLS is powdered based.
STEP 4
Settings and Considerations
Temperature affects the printing process heavily where the first layer is the most important step for most printing techniques. Ensure you have the correct settings depending your object.
STEP 5
Support Material
There are variations in support material options that are used to hold up parts of the object. Some are soluble in water and others require careful removal from the printed objects.
STEP 6
Post-processing
Post-processing can also include aesthetic modifications of the object, such as painting, sanding and polishing.
3D PRINTING TECHNOLOGIES
The current state of 3D printing is dominated by a number of techniques, each having a different procedure, materials, and performance and end product properties. The method chosen is dependent on the requirements by the user. The three most used are:
- Fused Filament Fabrication (FFF) or popularly known as Fused Deposition Modeling (FDM)
- Stereolithography (SLA)
- Selective Laser Sintering (SLS)
These 3 types differ mainly with the state of the raw materials before the printing process. FFF uses melted plastics, known as a filament, SLA uses a liquid resin as a starting base while SLS begins with a powder composite that is melted to form the model.
3D printing is used for 3 main applications:
RAPID PROTOTYPING
Many organizations use rapid prototyping to test concepts, form and fit for products. It allows a company to verify the product and test its viability.
TOOLING AND MOULDS
Tooling and moulding is the process of creating custom designed final products. This is often the case for complex products that require special machinery in production. Moulds are used to cast tools and can also be manufactured to create more prototypes.
DIRECT MANUFACTURING
Direct manufacturing is the creation of a product using 3D printers. As 3D printers improve and more materials become available, more companies are using direct manufacturing as part of their production process. The added advantage of 3D printing is it allows an organization to build custom parts for customers without having to restructure their complete production process.
FUSED FILAMENT FABRICATION
FFF is the most commonly used additive manufacturing method. It utilises a filament (coiled plastic) that is melted through a heated nozzle and the desired part is built layer by layer.
The printer consists of two nozzles able to move along the X and Y axis. Additionally, it includes a build tray that moves down as each layer is constructed. FFF is mainly used for rapid prototyping. The layer height range is between 0.04-0.4 millimetres.
This method is the most accessible since materials are affordable and so are the printers. Additionally, the wide range of materials is constantly being developed meaning more versatility will be possible in the future at a lower cost.
FFF DIAGRAM
Melted plastic based
FDM uses spools of plastic called filaments that are feed through an extruder. They come as a solid and are melted to create the object.
Multiple materials available
FDM has a wide range of materials to print with and each year more are added with the advancement of material science.
Requires support material
Complex objects with overhangs or bridges will require support material to hold up those areas and prevent deformation. ct using 3D printers. As 3D printers improve and more materials become available, more companies are using direct manufacturing as part of their production process. The added advantage of 3D printing is it allows an organization to build custom parts for customers without having to restructure their complete production process.
Materials and printers inexpensive
Both printers and materials for FDM are relatively affordable in comparison with other printing methods.
POPULAR FFF MATERIALS
ABS
About
ABS is a popular durable and flexible plastic. It is lightweight and is easy to work with and is already widely used in other mainstream products.
Applications
ABS is used for architectural models, concept product models, manufacturing, fixtures and general DIY projects.
Limitations
ABS has a high-temperature requirement and this can create fumes. This can be mitigated if the 3D printer comes with an air purification system.
PLA
About
PLA is a material derived from biodegradable compounds and is widely used in additive manufacturing. Being derived from natural sources means it is safer to use than ABS. Another great feature is PLA can be used with food which opens it up to the food industry and the medical industry.
Applications
Prototyping low-cost models and functional models.
Limitations
PLA is not as heat resistant as ABS and has a rough texture that can degrade over long periods of time.
PVA
About
PVA is a water-soluble plastic used in 3D printing primary as a support structure material in the construction of complex structures.
Applications
Used as a support material.
Limitations
PVA is an expensive material compared to the other plastics and can also release toxic fumes if the temperature settings are too high.
HIPS
About
HIPS is a filament that is very similar to ABS but unlike ABS, it is soluble in d-limonene. It also has the advantage of being lighter than ABS making it a useful filament for various applications.
Applications
HIPS is used both to build prototypes but has the additional benefit of being able to be a support material for complex prints.
Limitations
HIPS requires that your printer has both a heated bed and is capable of reaching high temperatures for effective printing.
PETG
About
PETG is a very durable material that is used in 3D printing. It has high strength and high heat resistance. Furthermore, it is safer than ABS when using it alongside food products or medical instruments.
Applications
PETG is used for prototyping models, functional prototypes and end-use products. It is also used for mechanical parts since it is not affected by shrinkage, warping and it is fairly flexible.
Limitations
Although highly durable, the disadvantage of using PETG is that it requires careful calibration to achieve high-quality prints.
NYLON
About
Nylon is utilized heavily due to its industrial strength, flexibility and durability. It is stronger than both ABS and PLA and additionally has the added advantage of being affordable.
Applications
Nylon is used for many applications due to its versatility. It is used for both prototyping, manufacturing, tooling and machine parts.
Limitations
Nylon requires proper storage because it absorbs moisture easily and can also produce fumes if exposed to high temperatures.
STEREOLITHOGRAPHY AND DIGITAL LIGHT PROCESSING
The SLA technique uses a photosensitive liquid resin that is hardened by using a light source. In contrast to FFF, an object is created through a build platform being lowered into the resin and a light source above or underneath hardening the material. The objects created are usually more accurate and smoother than FFF, however this method is mainly used for intricate small objects and has issues with larger objects. There are industrial options available, but these are mainly used for businesses that need custom parts for clients or custom tooling.
SLA DIAGRAM
Liquid resin based
SLA uses liquid resins that are solidified with a UV light.
Multiple materials available
There are various resins available. Either general or engineering based. Due to the nature of SLA, many companies produce their own resins but with similar properties to some filaments.
Requires support material
Some objects will require support material.
Printers are expensive
SLA printers are expensive in comparison to FDM printers. Additionally, the resins are priced higher than standard filaments.
POPULAR SLA MATERIALS
General Resins
About
Unlike FFF, SLA uses liquid resins that can be categorized by use and not specific material types. This is due to the variety of companies that produce their own variants and resin combinations.
General purpose resins have similar finishes to standard plastic and colour choices are limited.
Applications
General purpose resins have a number of standard uses. The main advantage they bring is they allow for high fidelity prototypes to be built. However, SLA has issues with building larger models. General purpose resins are used to produce, jewellery, functional prototypes and art models.
Limitations
SLA uses a variety of chemical solvents, and UV light which require safety precautions to be strictly followed.
Engineering Resins
About
Engineering resins can come with a number of attributes that are dependent on the development requirements. Some are similar to ABS (Tough), others have high-temperature resistance or overall durability. These type of resins are used for both rapid prototyping and also direct manufacturing.
Although these resins have various properties that aim to reproduce the durability of injection moulded parts, they can be expensive.
Applications
- Tough Resins: Prototypes and visual prototypes. These resins are designed for heavy use cases and case where the structure will be subjugated to high stress.
- High-temperature resistant resins: Tooling or moulds that require heat-resistant properties.
- Overall durable resins: Rapid prototyping and visual prototypes.
Limitations
- Tough Resin: Low heat resistance
- High-temperature resistant resin: Low strength.
- All resins require careful storage solutions.
SELECTIVE LASER SINTERING SLS
Selective Laser Sintering (SLS) is a method that uses a laser to solidify a powder material. It works by having a build area that is filled with a powder composite and storage compartment.
The small amount of powder in the build area is heated to just below its melting point by a laser. As the laser melts the first layer, the build platform moves down as the powder store area moves up. This action adds a new layer that can be melted by the laser.
The other powder that remains in the build area also acts as a support for the object. This method is suitable for functional components and end products. Generally, SLS is used with different polymer materials while metallic components are produced using DMLS (Direct metal laser sintering).
This process is similar but has different power requirements and slightly different processes due to the metal.
Traditionally SLS is a method that has been strictly used by large institutions due to the high price of an SLS printer.
SLS DIAGRAM
Powder resin based
SLS uses a powder based system that is melted with a laser.
Multiple materials available
SLS has the least materials available, however you can get metallic composites unlike other printing methods.
Does not require support material
SLS objects do not require support since they are submerged in the powder which supports the object as it is being built.
Printers are expensive
SLS printers, especially the metallic based are extremely expensive.
POPULAR SLS MATERIALS
Plastics
About
SLS printers can print using a variety of plastics to produce desired parts.
The most commonly used polymer is nylon, however, there are equivalent composites that have the properties of ABS, PLA and other standard printing plastics. Often glass or other materials are added in SLS powders to induce specific material requirements.
Applications
The applications for plastic powders for SLS are to produce a wide variety of standard prototypes, visual concepts and functional prototypes. These prototypes can have heat resistant properties or be flexible. One example is printing shoe components.
Limitations
SLS standard plastics have different properties and deficiencies.
Depending on the composite, the deficiencies are similar in nature to standard polymers. The variety of materials are limited however for SLS printing.
Metallic composites
About
There are metal composites like Alumide which is a composite of nylon and aluminium particles.
Like plastics, everything in terms of characteristics is dependent on end-user requirements. So long as the metal can be melted, then it is viable for DMLS.
Applications
Functional prototypes and tooling for aerospace, medicine, electronics and rapid manufacturing. The usage of these parts is for highly customizable situations that require unique engineering solutions that are not easily found in standard industry.
Limitations
Better materials are expensive depending on the composite.
SLS can be risky due to possible combustion due to the metals and powder inhalation.
Applications of 3D printers in Industry
Rapid prototyping is a method of quickly manufacturing prototypes of products or creating tooling quickly and cost-effectively. The goal for many product development teams is to reduce the lead time in the development process. Many companies face bottlenecks due to the need to ensure quality for the end product. Both designers and engineers need to create prototypes to ensure that there are no design flaws in the product. Prototyping allows the development team to demonstrate products to stakeholders, create debate on design choices and quickly redesign faulty prototypes. The advent of 3D printing has meant the process has evolved and allowed for a number of advantages over the standard methods.
Before the decision to start rapid prototyping with 3D printers, there are a number of questions that a product team needs to answer.
- What are the other options?
- What are the quality requirements for prototyping and which 3D printing technique to use?
- What are the resources that the team is willing to invest into rapid prototyping?
- Is 3D printing safe?
Rapid Prototyping Process
1. The research and planning stage involves information gathering and accurately defining the goals, the problem that the product will solve and objectives before the design phase.
2. The design phase involves creating product mock-ups and using CAD software to create a 3D object. Reiterations are carried out after the evaluation stage if problems are discovered.
3. Before the product can be built, a design review is carried out to better reach product goals and requirements.
4. After approval of the design, the build stage involves printing the design and then evaluating the object to see if it meets desired specifications. If issues are discovered, the process begins again before production.
Applications of 3D printers in Industry
Before 3D printing’s technological advances, two of the most popular standard prototyping methods have been injection moulding and CNC machining. These methods are all subtractive and have some limitations. They are usually expensive considering the material wastage and requirements of complex expensive machines to create an object.
CNC machining involves creating a CAD model, with a precise machining plan which is created to instruct the CNC machine on how to cut, mill or drill the raw material into the desired object. This process is time-consuming and many complex objects require multiple runs in order to meet the product specifications. Considering this process, if a reiteration for a product is needed, the process needs to be restarted. This method is extremely expensive and requires careful planning. The advantages are only felt when it comes to mass production but are limited during the product development stage.
Injection moulding is the process of creating parts using melted material by inserting it into a mould and then allowing it to harden. The process is widely used in manufacturing and has its own advantages and disadvantages. However, issues arise when it comes to prototyping since it is a large industrial process that requires special tools and is mainly used in the production of metal parts and plastics. The costs to benefit is limited during the product development stage and this method is slow when changes are required. A small or medium sized business cannot justify the cost in relation to benefit during the development of a product. Additionally, the handling of the molten material is a safety concern for many businesses. Safety precautions are implemented but accidents can still occur.
3D printing, unlike the previous methods, is the fastest technique for rapid prototyping. Lead times are significantly lower irrespective of product complexity and the costs are minimal.
What are the quality requirements for prototyping and which technique to use?
The second step in the rapid prototyping decision process is to make decisions regarding what kind of 3D printer to use depending on your fidelity requirements. In terms of complexity, all 3D printers can achieve complex geometries, unlike subtractive methods. For low fidelity concepts that involve more visual prototyping and basic functional prototypes with no specific requirements then the best choice would be FFF. FFF recently has made strides in quality and can create high-quality prints. Higher fidelity requirements can be achieved with SLA, however, the higher fidelity requirements mean more costs, both in materials and general operational costs. SLS can achieve medium fidelity models, mainly intricate small models and has the added bonus of metallic materials, but the investment requirements are the highest with printers being the main cost.
What are the resources that the team is willing to invest into rapid prototyping?
Resource decisions for 3D printing depending on:
- Technique choice
- Volume of printing parts
- Sizes of intended parts
- Material choice
- Post-Processing requirements
In terms of choice in printing techniques, FFF, as mentioned, is the most affordable. Printers start at US $1500 and prices go upwards for higher-end models. The higher-end models have features and capabilities to improve the quality of prints and better print quality. In terms of printing volume, FFF also has the largest capacity possibilities. The material costs also are relatively low with filaments starting around US $50, while the more expensive filaments, especially for engineering purposes can cost around US $100. This cost-benefit means a higher volume of printing can be achieved at a lower cost than the other printing technologies. FFF printers also come in a variety of sizes and have the largest advantage in printing larger models. The largest printers can build models over a meter long and post-processing is minimal with less waste than other printing technologies.
TECHNIQUE COMPARISON TABLE
| Attribute | FFF | SLA | SLS |
|---|---|---|---|
| Raw Material Used | Solid | Liquid | Powder |
| Raw Material Handling | Easy | Medium | Hard |
| Resolution | Low | High | Medium |
| Machine Costs | Low | Medium | High |
| Operation Costs | Low | High | Medium |
| Material Options | Many | Few | Few |
| Surface | Medium | Very Smooth | Smooth |
| Build Volume | Large | Small | Medium |
| Use | Easy | Intermediate | Intermediate |
| Print Complexity | High, with soluble support | High, with support | High |
| Support Structures | Can be removed by hand or by dissolving in water | Have to be remove by plier/cutter | None |
| Post Processing | Low to none | Medium, curing | Medium, removing powder |
| Time-to-market After Printing | Instant | Curing, 15 minutes | Removing powder, 10 minutes |
| Machine Preparation | Low, 5 minutes avg. | Very low, 1 minute avg. | Low, long heat up? |
| Machine After-care | Medium, 10 minutes avg. | Medium, 10 minutes avg. | Low, 15 minutes avg. |
| Recommended Protection | None | Gloves | Gloves, mask |
| Deformation | Gradually | Sudden | Gradually |
SLA printers are relatively expensive with prices ranging from US $3000 to over US $80000. Material costs, however, begin at around $150 for resins and as stated, prices increase as you purchase for higher fidelity requirements.
The volume capabilities of SLA are lower than the other printing techniques due to the need to cure the liquid resin. Additionally, the part sizes that can be printed are smaller than other printing technologies. This is due to the nature of the printing setup where many machines lift the object from the resin, therefore larger objects can be challenging to print.
There are reverse setup options where the laser is above and this allows the volume capacity to increase but at a cost. These printers incur large investment costs and management of the liquid resin in a large printer is difficult during the post-processing step.
SLS printers are the priciest, but they offer medium print quality. They are mainly for large organizations and pricing starts at US $10000 and can reach above US $500000 for industrial configuration printers. Material costs are also pricey, starting at US $100 and the metallic powder being the priciest. SLS printed parts can be larger than standard SLA, but smaller than FFF’s capacity. Select Laser Sintering is suitable for more high-fidelity oriented printing and is effective in the higher end production requirements for engineering companies. These requirements are for end-use products, functional prototypes at the end of the product development process before full-scale production can begin.
SLS printers are the priciest, but they offer medium print quality. They are mainly for large organizations and pricing starts at US $10000 and can reach above US $500000 for industrial configuration printers. Material costs are also pricey, starting at US $100 and the metallic powder being the priciest. SLS printed parts can be larger than standard SLA, but smaller than FFF’s capacity. Select Laser Sintering is suitable for more high-fidelity oriented printing and is effective in the higher end production requirements for engineering companies. These requirements are for end-use products, functional prototypes at the end of the product development process before full-scale production can begin.
SAFETY AND RISK
Before making a purchase of a 3D printers, the issue of safety is a major factor depending on intended use. Having machines that use heat, lasers and a multitude of different materials that can be mishandled is a risk that needs to be considered at every step of the prototyping process. Each development team needs to assess the usage frequency, the location of the printer, how well trained are the users and the safety features of the printer before making a purchase. Each printer has its safety concerns when it comes to usage and some need more safety training than others.
The following table highlights key areas of concern:
| Hazards | FFF | SLA | SLS |
|---|---|---|---|
| Material Handling | Low: Most filaments come in a solid coil and pose no immediate danger to the user. | Medium: SLA uses liquid resin with many mixtures that can cause irritation to eyes and skin. | High: Powder polymers can easily be inhaled and dropped leading to safety concerns for users. |
| Flammability | Low: Heated nozzles can reach high temperatures and should not be touched during operation. | Low: Liquid resins are low risk to flammability depending on handling. | High: Metallic powders do have a risk with combustion. |
| Toxicity | Low: ABS can produce fumes but many printers have air filters. | Medium: Mishandling of liquid resins is a danger and ingestion is hazardous. | Medium: Powder can get into sensitive areas and cause health concerns. |
| Inhalation | Low: Inhalation main arise from possible material fumes, but printers can be purchased with HEPA air filters. | Low: Resins need to be stored carefully and enclosed. | High: Powders can be inhaled before or after printing. |
| UV Radiation | None | High: UV radiation is a health risk. | Low: SLS mainly uses lasers to melt powder polymers. |
| Training requirements | Minimum | Medium | High |
